Pitaevskii Center on Bose-Einstein Condensation

Principal investigators: Iacopo Carusotto, Franco Dalfovo, Stefano Giorgini, Chiara Menotti, Alessio Recati, Sandro Stringari.

Postdocs: Soumik Bandyopadhyay, Carlos Benavides (Marie-Curie Fellow), Victor Colussi, Jeff Maki, Gabriele Spada

PhD students: Anna Berti, Kevin Geier, Marija Sindik

Main research field:

• THEORY OF BOSE GASES AND BOSE-EINSTEIN CONDENSATES
• THEORY OF FERMI GASES
• QUANTUM MIXTURES, QUANTUM IMPURITIES, POLARONS
• SUPERFLUIDITY AND SUPERSOLIDITY
• DIPOLAR GASES
• MULTICOMPONENT AND COHERENTLY COUPLED CONDENSATES
• LOW DIMENSIONAL SYSTEM
• MODELS FOR ATOMS IN OPTICAL LATTICES
• TOPOLOGICAL PHASES OF MATTER
• ANALOG MODELS

Methods: Basic tools of statistical mechanics; hydrodynamic equations and models; mean-field approaches like Gross-Pitaevskii theory, Bogoliubov equations, BCS theory; sum rules; Quantum Monte Carlo; Bose-Hubbard and Fermi-Hubbard models; Density Matrix Renormalization group; Tensor Networks.

Recent PhD theses:

• Daniele Contessi (2023), Data driven approach to detection of quantum phase transitions
• Matteo Sighinolfi (2022), Open quantum systems and ultracold atoms
• Santo Maria Roccuzzo (2021), Supersolidity in a dipolar quantum gas
• Miki Ota (2020), Sound propagation in dilute Bose gases
• Luca Parisi (2019), Mixtures of ultracold Bose gases in one dimension: A Quantum Monte Carlo study
• Fabrizio Larcher (2018), Dynamical excitations in low-dimensional condensates: sound, vortices and quenched dynamics
• Giulia De Rosi (2017), Collective oscillations of a trapped atomic gas in low dimensions and thermodynamics of one-dimensional Bose gas
• Alberto Sartori (2016), Dynamical properties of Bose-Bose Mixtures
• Luis A. Peña Ardila (2015), Impurities in a Bose-Einstein condensate using quantum Monte-Carlo methods: ground-state properties
• Giovanni Italo Martone (2014), Static and dynamic properties of spin-orbit-coupled Bose-Einstein condensates
• Zou Peng (2014), Mean-field theory for the dynamics of superfluid fermions in the BCS-BEC crossover
• Hou Yan-Hua (2013), Two-fluid Hydrodynamics of a quasi-1D unitary Fermi gas
• Marco Larcher (2013), Localization and spreading of matter waves in disordered potentials
• Natalia Matveeva (2013), Study of dynamic and ground-state properties of dipolar Fermi gases using mean-field and quantum Monte Carlo methods
• Gianluca Bertaina (2010), Study of Ultracold Fermi Gases in the BCS-BEC Crossover: Quantum Monte Carlo Methods, Hydrodynamics and Local Density Approximation
• Ingrid Bausmerth (2009), Fermi Mixtures: Effects of Engineered Confinements

A supersolid shows both solid and superfluid properties. By rotating it you can clearly see that the moment of inertia is strongly reduced due to the superfluid irrotational flow. Even when the global superfluid behaviour diseappers, the moment of inertia shows a reduction due to the single droplet (local) superfluidity. We have also characterized the behavior of quantized vortices, focusing on the supersolid regime. We have found in particular that (i) the angular momentum per particle associated with the vortex line is smaller than ℏ, reflecting the reduction of the global superfluidity; (ii) the nucleation in a rotating trap is triggered -- as for a standard condensate -- by the softening of the quadrupole mode; (iii) many vortices can be arranged into a honeycomb structure, which coexists with the triangular geometry of the supersolid lattice and persists during the free expansion of the atomic cloud. We have very recently provided a new protocol for the generation of vortices and their experimental detection.

References:
S. M. Roccuzzo, A. Gallemì, A. Recati, S. Stringari, arXiv:1910.08513, Phys. Rev. Lett. 124, 045702 (2020)
A. Gallemì, S. M. Roccuzzo, S. Stringari, A. Recati, arXiv:2005.05718, Phys. Rev. A 102, 023322 (2020)
Marija Sindik, Alessio Recati, Santo Maria Roccuzzo, Luis Santos, Sandro Stringari, arXiv:2206.14100, Phys. Rev. A 106, L061303 (2022)

We have developed the equivalent of Bogoliubov theory (for weakly interacting Bose gases) for the lattice models, but starting from the Gutzwiller ansatz. We find that the approach is extremely well suited to calculate the correlations of the systems. The model is benchmarked against the available QMC result. We develop the formalism for the single component Hubbard model as well as for the 2-component Hubbard model. We applied the new approach in the study of impurities problems. In particular we study the effect of strong correlation in the Hubbard bath and of the phase transition on the dephasing mdel, as well as on the properties of the Bose-lattice polaron problem.

Reference:
F. Caleffi, M. Capone, C. Menotti, I. Carusotto, A. Recati, arXiv:1910.08513, Phys. Rev. Research 2, 033276 (2020)
Fabio Caleffi, Massimo Capone, Ines de Vega, Alessio Recati, arXiv:2011.13757, New J. Phys. 23 033018 (2021)
V. E. Colussi, F. Caleffi, C. Menotti, A. Recati, arXiv:2110.13095 , SciPost Phys. 12, 111 (2022)
V. E. Colussi, F. Caleffi, C. Menotti, A. Recati, arXiv:2205.09857, Phys. Rev. Lett. 130, 173002 (2023)

We study the dynamical evolution of an inhomogeneous ultracold atomic gas quenched at different controllable rates through the Bose-Einstein condensation phase transition. We use a stochastic (projected) Gross-Pitaevskii equation. The results are consistent with the predictions of the homogeneous Kibble-Zurek mechanism and, at long evolution times, also with the experimental observations.

References:
I.-Kang Liu, S. Donadello, G. Lamporesi, G. Ferrari, S.-C. Gou, F. Dalfovo, N.P. Proukakis, arXiv:1712.08074, Commun. Phys. 1, 24 (2018)
I-Kang Liu, Jacek Dziarmaga, Shih-Chuan Gou, Franco Dalfovo, Nick P. Proukakis, arXiv:2004.09642, Phys. Rev. Research, in press (2020)